(1) Field of the Invention
Evaporation of refrigerant in cooling and freezing plants, refrigeration engineering, refrigeration machine for cooling and heating operation, refrigeration plants, refrigeration sets, heat pumps, air-conditioning systems and others.
(2) Description of the Related Art
Evaporator control with drive dry expansion on the basis of the minimum stable signal (MMS) is illustrated in (FIGS. 1, 2 and 3).
For optimum operation of an evaporator used in refrigeration, the evaporator is supplied with sufficient wet steam for a control valve (expansion valve) (3) to be controlled to a minimum stable signal, normally on the basis of the evaporator outlet pressure (12) and the associated evaporator outlet temperature (13) (drawing FIGS. 1, 2 and 3). The difference between the evaporator pressure, converted by calculation into the associated evaporation temperature, and the actual evaporation temperature measured is used as measured variable for the control valve. In this context, the aim is stable control characteristics with as low a temperature difference as possible. As low a temperature difference as possible leads to a higher evaporator power. If the difference is too low or the signal is not stable, liquid shocks or power reduction occur at the compressor (1). If the difference is too great, the evaporator power (4) is reduced.
Automatic valves, capillary tubes or other equipment are also dimensioned and used on the basis of the same principle (superheated refrigerant vapor at the end of the evaporation process).
Nowadays, in some cases internal heat exchangers (IHEs) (5) (FIG. 4, 5, 6) are connected downstream of the evaporator. However, these internal heat exchangers are designed as “thermally short” equipment and are not incorporated in the evaporator control on the basis of the entry vapor content. The refrigerant liquid is not strongly cooled and the suction vapors are not strongly superheated. The superheating of the suction vapor is restricted to approx. 5-10K. Injection valves which are customary nowadays are also not designed for maximum superheating, and the superheating which can be set is at most approx. 20-25K.